1. Field of the Invention
The present invention relates to a liquid discharging head configured to perform recording on a recording medium by discharging liquid droplets.
2. Description of the Related Art
One generally-used ink ejection method for a liquid discharging head of an ink jet recording apparatus is a method for discharging ink using an electrothermal conversion element. This method uses film boiling according to thermal energy of the electrothermal conversion element to eject ink within a bubble generating chamber from a discharging port. Ink is discharged as droplets in a direction generally orthogonal to the principal surface of an element substrate. A normal liquid discharging head is formed so that the center positions of the bubble generating chamber, electrothermal conversion element, and discharging port are located in the same position as viewed from a planar view.
When employing this ink discharging method, an air bubble generated by receiving thermal energy on the electrothermal conversion element grows to discharge ink, following which the thermal energy of the electrothermal conversion element and ink existing around the electrothermal conversion element diffuse, whereby the volume of the air bubble is reduced. At the same time, a liquid surface having a meniscus is formed within the discharging port after ink ejection, and this liquid surface descends inside the bubble generating chamber to compress the air bubble. Thus, there may be a case where the air bubble is split to form small split air bubbles, and these split air bubbles damage the surroundings of the air bubble at the time of the split air bubbles collapsing. Specifically, there may be a case where cavitation is generated due to driving of the electrothermal conversion element, and the surface of the electrothermal conversion element is damaged by influence thereof.
A liquid discharging head has been disclosed in Japanese Laid-Open No. 2008-238401 to deal with such cavitation. This liquid discharging head has a configuration wherein the position of the center of the discharging port is disposed on the downstream side from the center of the bubble generating chamber, in the direction of ink flowing into the bubble generating chamber from a supply path (ink flow path). The center of the discharging port is disposed on the downstream side rather than the center of the bubble generating chamber, and accordingly, distance between wall portions on the downstream side of the bubble generating chamber and an inner circumferential edge portion on the downstream side of the discharging port is reduced, and space is reduced. Thus, the air bubble is not readily split by the liquid surface having a meniscus after ink discharge. Accordingly, split air bubbles are not readily formed, and occurrence of cavitation is suppressed. Therefore, the surface of the electrothermal conversion element is not easily damaged, and durability of the liquid discharging head itself is improved.
However, the discharging port of the liquid discharging head is generally formed by patterning by exposure, and accordingly, there are cases where a discharging port is not formed at its predetermined position, due to misalignment at the time of manufacturing. Therefore, even there may be cases even with the configuration of the invention disclosed in Japanese Laid-Open No. 2008-238401 where the position where the discharging port is formed has deviated from the predetermined position, and the center thereof is closer to the center position of the bubble generating chamber. In such a case, as described above, an air bubble may be split by the liquid surface having meniscus after ink ejection, and split air bubbles may be formed. When the split air bubbles are formed, the surface of the electrothermal conversion element is damaged at the time of the split air bubbles collapsing.